South Korea's economic growth momentum has slowed considerably over the past year as Asia's fourth largest economy weathers the effects of slowing global growth and U.S.-China trade tensions, it added.

The rating agency said it forecasts South Korea's economic growth to slow to 2 percent in 2019 from 2.7 percent in 2018, noting the downturn in the semiconductor sector is driving a contraction in exports and weighing on facilities investment.

Semiconductors account for one-fifth of South Korea's outbound shipments.